1. Field of the Invention
The present invention relates to finely divided particles of water insoluble compounds that exhibit high negative zeta potentials at pH 7-8, small particle size, plus high adsorption of cationic material and compositions including such particles for use as drainage/retention aids in papermaking.
More particularly the present invention concerns sub-micron particles of metallic silicates such as crystalline sodium alumino silicates (zeolites) and amorphous sodium alumino silicates.
2. Brief Description of the Prior Art
The use of a variety of microparticle-based retention aids and drainage aids in systems that employ combinations of colloidal particles along with polymers such as cationic starches and/or synthetic cationic polymers is well established.
The pioneering system was EKA-Nobel's Composil.TM., based on colloidal silica and cationic potato starch. This was soon followed by Nalco's "Positek".TM. System based on colloidal silica, cationic potato starch and an anionic polymer. Other systems employ variants of these ingredients, including DuPont's work on silica-based microgels and Allied Colloid's "Hydracol".TM., system based on bentonite. These technologies provide materials which are combined in a novel way to enhance the paper-making process.
While the concept of retention aids is well understood from an electro-chemical point of view, finding effective, low cost microparticles that emulate the performance of silica or bentonite has proven difficult.
Conceptually, the role of microparticles in these systems is to provide a large number of very small point sources of anionic charge around which cationic polymers, fine paper fibers and fillers form into flocs which aid in their retention. These fast forming, shear sensitive flocs also represent areas of high solids consistency and, therefore, act as dewatering mechanisms when they are "captured" by larger fibers. Because of their small size, they enhance paper formation. The high retention of polymers that they provide translates into strength advantages in the finished paper.
The desirable properties of ideal microparticles are: high numbers of low cost, non-toxic, small particles with stable (&gt;20 millivolt) surface charges with a minimum impact on other paper making properties such as color, printability, porosity etc.
Presently, EKA-Nobel, Nalco and DuPont produce their own colloidal silicas in the United States and have provided retention aids systems for the paper industry based upon these silicas. Allied Colloids has a similar system which uses bentonite clay particles as a macroparticle in a competitive system.